Methods for verifying digital-electricity line integrity

ABSTRACT

The integrity of transmission-line voltage measurements in a digital-electricity power system in the presence of line-voltage disturbances during a sample period is ensured via detection or prevention by (a) acquiring at least three measurements of transmission-line voltage, performing numerical analysis on the measurements to produce a polynomial function, and estimating accuracy of the polynomial function based on magnitude of variance of the individual measurements; (b) applying a negative or positive bias to the transmission line during the sample period and acquiring voltage measurements to determine a rate of voltage change with the bias applied; (c) shifting a start time of a first sample period on a first transmission line in reference to a second sample period on a second transmission line to reduce overlap of sample periods across both transmission lines; and/or (d) synchronizing start times of respective sample periods on first and second transmission lines.

RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application No.62/490,389, filed 26 Apr. 2017, the entire content of which isincorporated herein by reference.

BACKGROUND

Digital electric power, or digital electricity, can be characterized asany power format where electrical power is distributed in discrete,controllable units of energy. Packet energy transfer (PET) is a new typeof digital electric power protocol disclosed in U.S. Pat. No. 8,068,937,U.S. Pat. No. 8,781,637 (Eaves 2012) and international patentapplication PCT/US2017/016870, filed 7 Feb. 2017.

The primary discerning factor in a digital power transmission systemcompared to traditional, analog power systems is that the electricalenergy is separated into discrete units; and individual units of energycan be associated with analog and/or digital information that can beused for the purposes of optimizing safety, efficiency, resiliency,control or routing. Since the energy in a PET system is transferred asdiscrete quantities, or quanta, it can be referred to as “digital power”or “digital electricity”.

As described in Eaves 2012, a source controller and a load controllerare connected by power transmission lines. The source controller ofEaves 2012 periodically isolates (disconnects) the power transmissionlines from the power source and analyzes, at a minimum, the voltagecharacteristics present at the source controller terminals directlybefore and after the lines are isolated. The time period when the powerlines are isolated was referred to by Eaves 2012 as the “sample period”,and the time period when the source is connected is referred to as the“transfer period”. The rate of rise and decay of the voltage on thelines before, during and after the sample period reveal if a faultcondition is present on the power transmission lines. Measurable faultsinclude, but are not limited to, short circuits, high line resistance orthe presence of an individual who has improperly come in contact withthe lines.

Eaves 2012 also describes digital information that may be sent betweenthe source and load controllers over the power transmission lines tofurther enhance safety or provide general characteristics of the energytransfer, such as total energy or the voltage at the load controllerterminals. One method for communications on the same digital-powertransmission lines as used for power was further described and refinedin U.S. Pat. No. 9,184,795 (Eaves Communication Patent).

One application of a digital-power distribution system is to safelydistribute direct-current (DC) power in digital format and at elevatedvoltage from the source side of the system to the load side.

U.S. Pub. Pat Application No. 2016/0134331 A1 (Eaves Power Elements)describes the packaging of the source side components of Eaves 2012, invarious configurations, into a device referred to as a digital powertransmitter.

U.S. Pat. No. 9,419,436 (Eaves Receiver Patent) describes the packagingof various configurations of the load side components of Eaves 2012 intoa device referred to as a digital power receiver.

SUMMARY

The methods described, below, build on the earlier work of Eaves 2012 byfocusing on novel methods to minimize errors in the detection of a faulton the transmission lines. Such errors can be caused by electrical noiseor other disturbances that can affect the integrity of the data beingsensed from the transmission lines when executing the packet energytransfer protocol.

Digital electric power, or digital electricity, can be characterized asany power format where electrical power is distributed in discrete,controllable units of energy. A digital electricity system periodicallyisolates an electrical transmission line from both the source and loadto analyze analog line characteristics that reflect a possible fault orhuman contact with the transmission wiring. The detection of line faultsinvolves periodic measurement of transmission-line voltage. However,practical transmission-line voltage measurements often are influenced byelectrical noise or unwanted oscillation. The disclosed methods can beused to ensure the integrity of the analog measurements used for faultdetection, thus preventing falsely positive or falsely negativeline-fault determinations.

Methods for ensuring the integrity of the data used in determiningtransmission-line faults while executing packet energy transfer aredescribed herein, where various embodiments of the methods and apparatusfor performing the method may include some or all of the elements,features and steps described below.

In embodiments of the method for ensuring the integrity oftransmission-line voltage measurements in a digital-electricity powersystem comprising one or more transmitters, voltage on one or more ofthe transmission lines is monitored and controlled with a respectivetransmitter. The integrity of transmission-line voltage measurements inthe presence of line-voltage disturbances during a sample period isensured by employing at least one of the following four methods.

In a first method, at least three measurements of transmission-linevoltage are acquired during the sample period where voltage measurementsmay be affected by electrical disturbances. Numerical analysis isperformed on the measurements to produce a polynomial function thatapproximates disturbance-free transmission-line voltage measurements.The accuracy of the polynomial function is estimated based on themagnitude of variance of the individual measurements from theapproximation, and the transmission-line power is interrupted if theestimated accuracy does not meet a minimum accuracy requirement.

In a second method, a negative or positive bias is applied to thetransmission line during the sample period. Voltage measurements areacquired to determine a rate of voltage change with the bias applied;and power to the transmission line is interrupted if the rate of voltagechange is outside of predetermined minimum and maximum values.

In a third method, where the digital-electricity power system comprisesat least a first and a second transmission line, a start time of a firstsample period on the first transmission line is shifted in reference toa second sample period on the second transmission line to reduce overlapof sample periods across both transmission lines to prevent induction ofelectromagnetic noise from one transmission line to another transmissionline.

In a fourth method, where the digital-electricity power system comprisesat least a first and a second transmission line, a start time of a firstsample period on the first transmission line is synchronized with astart time of a sample period on the second transmission line to allowelectromagnetic noise from both transmission lines to decay to anacceptable value before the end of the sample period, thus leaving atleast part of the remaining sample period available for disturbance-freevoltage measurement.

In executing the packet energy transfer (PET) protocol inherent todigital electricity, a portion of the total energy packet period isallocated for the transfer of energy from the source to the load. Thisportion is referred to as the transfer period. The remaining time in thepacket period is allocated for detecting faults and transferring data.This portion of the packet is referred to as the sample period. In oneembodiment, the controller on the source side of the system monitors thedecay in transmission line voltage during the sample period. A change inthe rate of decay can indicate a variety of fault conditions, includinga short circuit or human contact with the transmission-line conductors.

There are a number of practical considerations related to ensuring theintegrity of fault detection within the PET protocol. The firstconsideration is obtaining valid measurements of transmission-linevoltage during the sample period when there are oscillations on thetransmission lines due to “reflected waves”. Reflected waves occur whena pulse of electrical current travels to the end of the line and isreflected back to the original location. The reflections will appear asvoltage oscillations when observed at any point in the transmissionline. The oscillations can cause errors in the determination of thedecay rate of the line voltage during the PET sample period.

A second consideration is excessive line-to-line capacitance associatedwith long transmission lines. The capacitance can reach a level where itshrouds the effects of a decrease in line-to-line resistance.

A third consideration is the coupling of electromagnetic interference(EMI) to the transmission-line pairs. The interference can originatefrom other transmission-line pairs in close proximity, including otherdigital-electricity transmission-line pairs.

Methods described herein address these considerations through bothprevention and detection.

From a prevention standpoint, multiple parallel transmission linestransmitting digital electricity are interleaved, meaning that the startof the energy packet in one transmission line is purposely shifted intime in relation to other transmission lines. Specifically, the sampleperiods of multiple energy packets are, as much as is practical,arranged so that they do not occur at the same time in transmissionlines that are in close proximity. As will be described in more detail,below, transmission-line reflections produce oscillations that are asource of EMI; and the EMI can produce disturbances in adjacenttransmission-line pairs. The line reflections are stimulated by thesudden decrease in line current caused by the start of the sampleperiod. Adjacent transmission lines containing digital electricity aremost susceptible to being disturbed by EMI if it occurs during thesample period because the transmission-line series impedance is muchhigher in this portion of the energy packet, meaning that EMI can begenerated with less energy.

Two detection methods are described herein.

The first detection method uses a biasing circuit to drive thetransmission-line pair to a desired voltage. The simplest form of abiasing circuit is a resistive voltage divider. By measuring thetransmission-line voltage while the bias is applied over a known timeperiod, a value indicative of the line-to-line impedance can becalculated. If the value is outside of predetermined acceptable values,a fault will be registered and power to the transmission lines will beinterrupted. In addition to detecting a fault on the transmission lines,the measurement is also useful for detecting hardware problems, such asa short-circuit failure of a line-disconnect device. If theline-disconnect device is unsuccessful in interrupting current to thetransmission line, the line voltage will not decay during themeasurement period, indicating a damaged disconnect device or supportingcircuitry.

Because the lines are being actively biased to a target voltage, themethod can overcome some of the effects of EMI or high capacitance onthe transmission lines. A trade-off for using biasing versus simplyopening the source-disconnect switch is that the biasing current canshroud the effects of a low current line-to-line fault on thetransmission lines since the system must distinguish the differencebetween the fault current and bias current to properly register a fault.

The second detection method involves determining if the voltage beingmeasured on the transmission lines during the sample period is too noisyto support a valid measurement. Referred to as anomaly detection, themethod quantifies the deviation of the transmission-line voltage duringthe sample period from an ideal reference line. If the deviation exceedsa predetermined maximum, the measurement is considered invalid. After apredetermined number of invalid measurements, the line is considered tobe in a faulted state and power to the transmission line will beinterrupted.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an embodiment of the safepower-distribution system.

FIG. 2 is an illustration of a packet-energy-transfer voltage (PETvoltage) waveform.

FIG. 3 illustrates the effect of line oscillations on the PET voltagewaveform.

FIG. 4 illustrates interleaving of two PET voltage waveforms.

FIG. 5 illustrates how one PET waveform can induce noise on an adjacentwaveform.

FIG. 6 illustrates the limitations in interleaving three PET waveforms.

FIG. 7 illustrates combined interleaving and synchronization of threePET waveforms.

FIG. 8 is a block diagram of a PET system with synchronization signals.

FIG. 9 illustrates the effects of high line capacitance in the PETwaveform.

In the accompanying drawings, like reference characters refer to thesame or similar parts throughout the different views; and apostrophesare used to differentiate multiple instances of the same item ordifferent embodiments of items sharing the same reference numeral. Thedrawings are not necessarily to scale; instead, an emphasis is placedupon illustrating particular principles in the exemplificationsdiscussed below. For any drawings that include text (words, referencecharacters, and/or numbers), alternative versions of the drawingswithout the text are to be understood as being part of this disclosure;and formal replacement drawings without such text may be substitutedtherefor.

DETAILED DESCRIPTION

The foregoing and other features and advantages of various aspects ofthe invention(s) will be apparent from the following, more-particulardescription of various concepts and specific embodiments within thebroader bounds of the invention(s). Various aspects of the subjectmatter introduced above and discussed in greater detail below may beimplemented in any of numerous ways, as the subject matter is notlimited to any particular manner of implementation. Examples of specificimplementations and applications are provided primarily for illustrativepurposes.

Unless otherwise defined, used or characterized herein, terms that areused herein (including technical and scientific terms) are to beinterpreted as having a meaning that is consistent with their acceptedmeaning in the context of the relevant art and are not to be interpretedin an idealized or overly formal sense unless expressly so definedherein.

The terminology used herein is for the purpose of describing particularembodiments and is not intended to be limiting of exemplary embodiments.As used herein, singular forms, such as “a” and “an,” are intended toinclude the plural forms as well, unless the context indicatesotherwise. Additionally, the terms, “includes,” “including,” “comprises”and “comprising,” specify the presence of the stated elements or stepsbut do not preclude the presence or addition of one or more otherelements or steps.

A representative digital-power system, as originally described in Eaves2012, is shown in FIG. 1 . The system comprises a source 1 and at leastone load 2. The PET protocol is initiated by an operating switch 3 toperiodically disconnect the source from the power transmission lines.When the switch is in an open (non-conducting) state, the lines are alsoisolated by isolation diode (D₁) 4 from any stored energy that mayreside at the load 2.

Eaves 2012 offered several versions of alternative switches that canreplace D₁, and all versions can produce similar results when used inthe presently described methods. Capacitor (C₃) 5 is representative ofan energy-storage element on the load side of the circuit.

The transmission lines have inherent line-to-line resistance (R₄) 6 andcapacitance (C₁) 7. The PET system architecture, as described by Eaves2012, adds additional line-to-line resistance (R₃) 8 and capacitance(C₂) 9. At the instant switch 3 is opened, C₁ and C₂ have stored chargethat decays at a rate that is inversely proportional to the additivevalues of R₄ and R₃. Capacitor (C₃) 5 does not discharge through R₃ andR₄ due to the reverse-blocking action of isolation diode (D₁) 4. Theamount of charge contained in capacitors (C₁ and C₂) is proportional tothe voltage across them and can be measured at points 16 and 17 by asource controller 18 or load controller 19.

As described in Eaves 2012, a change in the rate of decay of the energystored in C₁ and C₂ can indicate that there is a cross-line fault on thetransmission lines. The difference between normal operation and a fault,as presented by Eaves 2012, is illustrated in FIG. 2 .

Referring again to FIG. 1 , the combination of switch (S1) 3; sourcecontroller 18; resistor (R₁) 10; switch (S2) 11; and resistor (R₃) 8 canbe referred to as a transmitter 20. The combination of switch (S4) 15;resistor (R₅) 14; load controller 19; diode (D₁) 4; capacitor (C₂) 9;and capacitor (C₃) 5 can be referred to as a receiver 21.

FIG. 3 illustrates a first practical consideration when performingPET-oscillation in the transmission line voltage due to reflections orEMI. The oscillation affects the integrity of fault detection, raisingthe difficulty of extracting the rate of voltage decay due to the normaldepletion of energy in the line capacitance from the disturbances causedby the oscillations. Since the abnormal-decay transmission-line voltageduring the sample period indicates a transmission fault, the oscillationcan produce either a false positive or false negative test result. Whenthe amplitude of the oscillation is small, analog or digital filteringcan improve the measurement; but if the oscillation is large, the analogmeasurements become unusable.

The oscillations shown in FIG. 3 can originate from electromagneticinterference external to the transmission lines or from othertransmission-line pairs in close proximity, including otherdigital-electricity transmission-line pairs. In particular, longertransmission lines are subject to “reflected waves,” where a pulse ofelectrical current will travel to the end of the line and then reflectback to the original location. The reflections will appear as voltageoscillations when observed at any point in the transmission line. Theelectromagnetic emissions from transmission-line reflections in closelyadjacent digital-electricity line pairs can exacerbate the oscillations.Adjacent transmission lines containing digital electricity are mostsusceptible to being disturbed by EMI if it occurs during the sampleperiod, because the transmission-line impedance is much higher in thisportion of the energy packet, allowing disturbances to be set up withless energy.

As previously summarized, the methods described herein can apply bothprevention and detection methods to manage the practical operatingaspects of digital electricity on transmission lines.

A method of preventing oscillation interference is illustrated in FIG. 4, where two adjacent digital electricity transmission line pairs areoff-set, or interleaved, in time such that their sample periods do notoccur simultaneously. This off-set allows the oscillations to diminishbefore the end of the sample period, as exemplified at point 26,allowing a valid measurement of line decay once the oscillationamplitude falls to an acceptable level. Without interleaving, the sampleperiods can overlap; and the electromagnetic emissions from the firstline pair can extend the oscillations of the second, possibly until theoscillations consume the entire sample period as illustrated at point 28of FIG. 5 .

An acceptable, but less desirable, method to control line oscillationsis to synchronize the energy packets of two transmission lines such thatthe sample periods start simultaneously. In this way, the lineoscillations will occur and decay at approximately the same rate,allowing time later in the sample periods to make measurements when theoscillations have decayed to an acceptable level.

In practice, with large numbers of transmission line pairs, bothsynchronization and interleaving techniques can be employed, since, asthe number of transmission line pairs increases, it becomes impossibleto avoid overlap using interleaving techniques, alone. In the example ofFIG. 6 , it is not possible to offset more than the twotransmission-line packets shown, since there would be no remainingsample periods in any of the three waveforms that would not be affectedby the beginning of a sample period in another adjacent transmissionline. The overlap would again extend the oscillation 28 during thesample period. To resolve this issue, the sample period for two of thetransmission lines can be synchronized and the third can be off-set orinterleaved, as illustrated in FIG. 7 .

Referring to FIG. 1 , to facilitate the interleaving function, thetransmitters of this embodiment incorporate a synchronization input tothe source controller 18. Referring to FIG. 8 , in a particularembodiment, a master controller 30 generates a synchronization signalthat can be in the form of a pulse waveform or data element embedded ina serial communications stream. Each transmitter 20, 20′, 20″ holds anidentifier in its individual controller that associates the controllerto its respective transmission line 32, 32′, 32″. When the transmittercontroller detects the synchronization pulse, it applies the appropriateoffset to the start-time of the energy packet according to thesequential position of its transmission line among the transmission linegroup 32, 32′, 32″.

FIG. 9 illustrates a second consideration when performing measurementsduring the sample period. The decay of the transmission-line voltageduring the sample period can be very small when the transmission-linecapacitance is high versus lower-capacitance lines, as indicated by thedecay in FIG. 9 at point 34. This makes line-to-line fault detectionless sensitive, possibly leading to missing a fault condition.

FIG. 1 helps illustrate a first method for detecting high linecapacitance and other line-to-line faults. Adding line bias providesadditional current to charge or discharge the line capacitance. Sourcecontroller 18 acts to close solid-state switch (S3) 13 that connectsresistor (R₂) 12 across the transmission-line conductors. This providesa negative bias to the transmission lines through the “pull-down” effectof R₂. Another bias circuit that provides a greater range of control ofthe bias voltage set-point can be created by simultaneously closingsolid-state switch (S3) 13 and solid-state switch (S2) 11, which forms avoltage divider on the transmission line positive comprising resistor(R1) 10 and resistor (R2) 12.

The rate of voltage decay during the sample period with the bias appliedis then compared to predetermined maximum and minimum values. If therate of decay is too high or too low (i.e., above the predeterminedmaximum or below the predetermined minimum), the decay rate isindicative of a line fault. A fault because of high decay may be due tohuman contact or a foreign object placed across the transmission lines.A low decay fault may be due to excessive line capacitance or a hardwarefailure. The source controller 18 can then act to interrupt current tothe transmission line by opening disconnect switch (S1) 3.

A second detection method involves determining if the voltage beingmeasured on the transmission lines during the sample period is too noisyto support a valid measurement. Referred to as anomaly detection, themethod quantifies the deviation of the transmission line voltage duringthe sample period from an ideal reference line. If the deviation exceedsa predetermined maximum, the measurement is considered invalid. After apredetermined number of invalid measurements, the line is considered tobe in a faulted state; and power to the transmission line will beinterrupted. The preferred method is to accumulate a series of voltagesamples during the sample period and to compare the samples to anotional, non-vertical straight line using numerical regression, asillustrated in FIG. 3 by dotted line 24. The line represents the normaldecay rate of the transmission lines if the lines were undisturbed byline reflections or electromagnetic interference (EMI). There aremultiple methods for performing linear numerical regression well knownto those skilled in the art. One method that can be employed in thecurrent approach is the “least squares” method. If there is very littleEMI or line oscillation, very little variance will exist between thenotional line and the actual data samples since most data samples willfall very closely to the line. In instances of noisy or oscillatingtransmission lines, the variance or “residual” will be high; since manyof the samples will fall far from the notional line. The coefficient ofdetermination (r²) commonly applied to linear regression is used topredict if the notional line can viably be used as a model for theunderlying actual decay rate of the transmission lines during the sampleperiod and is expressed as follows:r ²=Cov(x,y)²/[Var(x)²·Var(y)²],where:

-   -   r² is the coefficient of determination;    -   x is the time of the sample relative to the start of the sample        period;    -   y is the voltage value of the sample taken at time x;    -   Cov(x,y) is the covariance of x and y;    -   Var(x) is the variance of x; and    -   Var(y) is the variance of y.

The calculations for variance and covariance are well known to thoseskilled in the art of numerical regression. Low values of r² mean thatthe notional line is not a viable model for the underlying decay of thetransmission-line voltage. If the value of r² falls below apredetermined value, a fault will be registered by the sourcecontroller; and the source controller will act to interrupt power to thetransmission lines.

Summary, Ramifications and Scope:

The source controller 18 and load controller 19 can include a logicdevice, such as a microprocessor, microcontroller, programmable logicdevice or other suitable digital circuitry for executing the controlalgorithm. The load controller 19 may take the form of a simple sensornode that collects data relevant to the load side of the system and doesnot necessarily require a microprocessor.

The controllers 18 and 19 can be computing devices, and the systems andmethods of this disclosure can be implemented in a computing systemenvironment. Examples of well-known computing system environments andcomponents thereof that may be suitable for use with the systems andmethods include, but are not limited to, personal computers, servercomputers, hand-held or laptop devices, tablet devices, smart phones,multiprocessor systems, microprocessor-based systems, set top boxes,programmable consumer electronics, network PCs, minicomputers, mainframecomputers, distributed computing environments that include any of theabove systems or devices, and the like. Typical computing systemenvironments and their operations and components are described in manyexisting patents (e.g., U.S. Pat. No. 7,191,467, owned by MicrosoftCorp.).

The methods may be carried out via non-transitory computer-executableinstructions, such as program modules. Generally, program modulesinclude routines, programs, objects, components, data structures, and soforth, that perform particular tasks or implement particular types ofdata. The methods may also be practiced in distributed computingenvironments where tasks are performed by remote processing devices thatare linked through a communications network. In a distributed computingenvironment, program modules may be located in both local and remotecomputer storage media including memory storage devices.

The processes and functions described herein can be non-transitoriallystored in the form of software instructions in the computer. Componentsof the computer may include, but are not limited to, a computerprocessor, a computer storage medium serving as memory, and a system busthat couples various system components including the memory to thecomputer processor. The system bus can be of any of several types of busstructures including a memory bus or memory controller, a peripheralbus, and a local bus using any of a variety of bus architectures.

The computer typically includes one or more a variety ofcomputer-readable media accessible by the processor and including bothvolatile and nonvolatile media and removable and non-removable media. Byway of example, computer-readable media can comprise computer-storagemedia and communication media.

The computer storage media can store the software and data in anon-transitory state and includes both volatile and nonvolatile,removable and non-removable media implemented in any method ortechnology for storage of software and data, such as computer-readableinstructions, data structures, program modules or other data.Computer-storage media includes, but is not limited to, RAM, ROM,EEPROM, flash memory or other memory technology, CD-ROM, digitalversatile disks (DVD) or other optical disk storage, magnetic cassettes,magnetic tape, magnetic disk storage or other magnetic storage devices,or any other medium that can be used to store the desired informationand that can be accessed and executed by the processor.

The memory includes computer-storage media in the form of volatileand/or nonvolatile memory such as read only memory (ROM) and randomaccess memory (RAM). A basic input/output system (BIOS), containing thebasic routines that help to transfer information between elements withinthe computer, such as during start-up, is typically stored in the ROM.The RAM typically contains data and/or program modules that areimmediately accessible to and/or presently being operated on by theprocessor.

The computer may also include other removable/non-removable,volatile/nonvolatile computer-storage media, such as (a) a hard diskdrive that reads from or writes to non-removable, nonvolatile magneticmedia; (b) a magnetic disk drive that reads from or writes to aremovable, nonvolatile magnetic disk; and (c) an optical disk drive thatreads from or writes to a removable, nonvolatile optical disk such as aCD ROM or other optical medium. The computer-storage medium can becoupled with the system bus by a communication interface, wherein theinterface can include, e.g., electrically conductive wires and/orfiber-optic pathways for transmitting digital or optical signals betweencomponents. Other removable/non-removable, volatile/nonvolatile computerstorage media that can be used in the exemplary operating environmentinclude magnetic tape cassettes, flash memory cards, digital versatiledisks, digital video tape, solid state RAM, solid state ROM, and thelike.

The drives and their associated computer-storage media provide storageof computer-readable instructions, data structures, program modules andother data for the computer. For example, a hard disk drive inside orexternal to the computer can store an operating system, applicationprograms, and program data.

The synchronization signal to either synchronize or offset the PETwaveforms described herein and illustrated in FIG. 6 can also begenerated by one of the source controllers controlling transmissionlines 32, 32′, 32″, thus eliminating the need for a separate mastercontroller. The source controller producing the signal would become themaster. There are several methods to determine which controller is themaster. For example, the source controller with the lowest serial numbercan assume the master duties.

The bias circuit described herein can be constructed using an activepower supply or operational amplifier circuit designed to drive thetransmission-line voltage to a predetermined voltage setpoint. Althoughmore complex than the simple voltage-divider circuit, an active device,such as an operational amplifier, is capable of driving thetransmission-line voltage to the target setpoint more quickly than aresistive voltage divider.

An alternative method to construct a resistive voltage divider biascircuit is to employ a partially enhanced solid-state switch 3 (such asS1 of FIG. 1 ). If the switch (S1) 3 is embodied as ametal-oxide-semiconductor field-effect transistor (MOSFET), the deviceis partially enhanced by using a lower than normal gate drive voltage.In a partially enhanced state, the MOSFET performs like a resistor.

The linear regression method described herein for deriving a notionalline of transmission-line decay can also be accomplished throughanalog-filtering circuitry or a digital-filtering algorithm. Linearregression is described in this specification due to the minimalprocessor resources necessary in the source controller to execute thealgorithm. However, there are many numerical regression techniques thatcan be employed that are well known to those skilled in the art. Thesecan be generally classified into linear, multi-linear and non-linearnumerical regression.

In describing embodiments of the invention, specific terminology is usedfor the sake of clarity. For the purpose of description, specific termsare intended to at least include technical and functional equivalentsthat operate in a similar manner to accomplish a similar result.Additionally, in some instances where a particular embodiment of theinvention includes a plurality of system elements or method steps, thoseelements or steps may be replaced with a single element or step.Likewise, a single element or step may be replaced with a plurality ofelements or steps that serve the same purpose. Moreover, while thisinvention has been shown and described with references to particularembodiments thereof, those skilled in the art will understand thatvarious substitutions and alterations in form and details may be madetherein without departing from the scope of the invention. Furtherstill, other aspects, functions, and advantages are also within thescope of the invention; and all embodiments of the invention need notnecessarily achieve all of the advantages or possess all of thecharacteristics described above. Additionally, steps, elements andfeatures discussed herein in connection with one embodiment can likewisebe used in conjunction with other embodiments. The contents ofreferences, including reference texts, journal articles, patents, patentapplications, etc., cited throughout the text are hereby incorporated byreference in their entirety for all purposes; and all appropriatecombinations of embodiments, features, characterizations, and methodsfrom these references and the present disclosure may be included inembodiments of this invention. Still further, the components and stepsidentified in the Background section are integral to this disclosure andcan be used in conjunction with or substituted for components and stepsdescribed elsewhere in the disclosure within the scope of the invention.In method claims (or where methods are elsewhere recited), where stagesare recited in a particular order—with or without sequenced prefacingcharacters added for ease of reference—the stages are not to beinterpreted as being temporally limited to the order in which they arerecited unless otherwise specified or implied by the terms and phrasing.

What is claimed is:
 1. A method for ensuring integrity oftransmission-line voltage measurements in a digital-electricity powersystem comprising one or more transmitters, the method comprising: witheach transmitter, monitoring and controlling voltage ofdigital-electricity power transmission on a respective transmissionline, wherein the digital-electricity power comprises energy packets;and ensuring integrity of transmission-line voltage measurements in thepresence of line-voltage disturbances during a sample period by using abias circuit distinct from transmission-line capacitance to apply anegative or positive bias to the transmission line during the sampleperiod; acquiring voltage measurements with the bias applied;determining a rate of voltage change with the bias applied; andinterrupting the transmission of digital-electricity power over thetransmission line when the rate of voltage change is outside ofpredetermined minimum and maximum values, including interrupting thetransmission of digital-electricity power over the transmission linewhen the rate of voltage change is below the predetermined minimum dueto excessive line capacitance.
 2. The method of claim 1, wherein theintegrity of the transmission-line voltage measurements in the presenceof line-voltage disturbances during the sample period is further ensuredby acquiring at least three measurements of transmission-line voltageduring the sample period where voltage measurements may be affected byelectrical disturbances; performing numerical analysis on the voltagemeasurements to produce a polynomial function that approximatesdisturbance-free transmission-line voltage measurements; estimatingaccuracy of the polynomial function based on magnitude of variance ofthe individual voltage measurements from the approximation, andinterrupting the transmission of digital-electricity power over thetransmission line if the estimated accuracy does not meet a minimumaccuracy requirement.
 3. The method of claim 2, where the numericalanalysis of the voltage measurements is a form of non-linear regression.4. The method of claim 2, where the numerical analysis of the voltagemeasurements is a form of digital filtering.
 5. The method of claim 2,where a signal indicative of the digital-electricity power is passedthrough an analog filtering circuit before the voltage of thedigital-electricity power is measured for use in the numerical analysis.6. The method of claim 1, where the bias is produced by an operationalamplifier circuit.
 7. The method of claim 1, where the bias is producedby a voltage-divider circuit.
 8. The method of claim 7, where at leastone resistance value in the voltage-divider circuit is produced bycontrolling the resistance of a transistor.
 9. The method of claim 1,where the bias is produced by a power-supply circuit.
 10. The method ofclaim 2, where the numerical analysis of the voltage measurements is aform of linear regression.
 11. The method of claim 1, where the one ormore transmitters comprise at least a first transmitter and a secondtransmitter, where the digital-electricity power system comprises atleast a first and a second transmission line, where the firsttransmitter includes a controller that applies an off-set to a starttime for transmission of energy packets on the first transmission line,where the second transmitter includes a controller that applies anoff-set to a start time for transmission of energy packets on the secondtransmission line, and wherein the integrity of the transmission-linevoltage measurements in the presence of line-voltage disturbances duringthe sample periods is further ensured by the off-sets applied by thecontrollers of the first and second transmitters shifting a start timeof the sample period for voltage measurements on the first transmissionline in reference to a sample period for voltage measurements on thesecond transmission line to reduce overlap of the sample periods acrossboth transmission lines to prevent induction of electromagnetic noisefrom one transmission line to another transmission line.
 12. The methodof claim 1, where the one or more transmitters comprise at least a firsttransmitter and a second transmitter, where the first transmitterincludes a controller that applies an off-set to a start time fortransmission of energy packets on the first transmission line, where thesecond transmitter includes a controller that applies an off-set to astart time for transmission of energy packets on the second transmissionline, and wherein the integrity of the transmission-line voltagemeasurements in the presence of line-voltage disturbances during thesample periods is further ensured by the off-sets applied by thecontrollers of the first and second transmitters synchronizing a starttime of the sample period for voltage measurements on the firsttransmission line with a start time of the sample period for voltagemeasurements on the second transmission line to allow electromagneticnoise from both transmission lines to decay to a diminished value beforethe end of the sample periods, thus leaving at least part of theremaining sample periods available for disturbance-free voltagemeasurement.